/*
 * Copyright (c) 1987, 1993
 *	The Regents of the University of California.  All rights reserved.
 * 
 * Portions copyright (c) 1999, 2000
 * Intel Corporation.
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 * 
 *    This product includes software developed by the University of
 *    California, Berkeley, Intel Corporation, and its contributors.
 * 
 * 4. Neither the name of University, Intel Corporation, or their respective
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS, INTEL CORPORATION AND
 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS,
 * INTEL CORPORATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#ifndef lint
static char sccsid[] = "@(#)tan.c	8.1 (Berkeley) 6/4/93";
#endif /* not lint */

#include "trig.h"
double
tan(x)
double x;
{
	double a,z,ss,cc,c;
	int k;

	if(!finite(x))		/* tan(NaN) and tan(INF) must be NaN */
		return x-x;
	x = drem(x,PI);			/* reduce x into [-PI/2, PI/2] */
	a = copysign(x,one);		/* ... = abs(x) */
	if (a >= PIo4) {
		k = 1;
		x = copysign(PIo2-a,x);
	}
	else {
		k = 0;
		if (a < small) {
			c=big+a;
			return x;
		}
	}
	z = x*x;
	cc = cos__C(z);
	ss = sin__S(z);
	z *= half;			/* Next get c = cos(x) accurately */
	c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
	if (k == 0)
		return x+(x*(z-(cc-ss)))/c;	/* ... sin/cos */
#ifdef national
	else if (x == zero)
		return copysign(fmax,x);	/* no inf on 32k */
#endif	/* national */
	else
		return c/(x+x*ss);		/* ... cos/sin */
}
